IoTivity-Constrained: IoT for tiny devices Kishen Maloor Open IoT Summit North America 2017

Overview •  Introduction •  Background in OCF •  Constrained environment characteristics •  IoTivity-Constrained architecture •  Porting IoTivity-Constrained •  Building Applications

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•  Open Connectivity Foundation (OCF) •  Publish open IoT standards

•  IoTivity-Constrained •  Small foot-print implementation of OCF standards

•  Runs on resource-constrained devices and small OSes

•  Quickly customize to any platform

Introduction

OCF standards A brief background

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•  RESTful design: Things modeled as resources with properties and methods

•  CRUDN operations on resources (GET / OBSERVE, POST, PUT, DELETE)

•  OCF roles

•  Server role: Exposes hosted resources

•  Client role: Accesses resources on a server

OCF resource model

Resource URI rt: Resource Type if: Resource Interface p: Policy n: Resource Name

Pro

pert

ies�

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Refer to the OCF Core spec at https://openconnectivity.org/resources/specifications

OCF “well-known” resources Functionality Fixed URI

Discovery /oic/res

Device /oic/d

Platform /oic/p

Security /oic/sec/*

… …

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•  Messaging protocol: CoAP (RFC 7252)

•  Data model: CBOR (RFC 7049) encoding of OCF payloads

•  Security model: DTLS-based authentication, encryption and access control*

•  Transport: UDP/IP; being adapted to Bluetooth

*Refer to the OCF Security spec at https://openconnectivity.org/resources/specifications

OCF protocols

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Resource discovery

Unicast response

[URI: /a/light; rt = [“oic.r.light”], if = [“oic.if.rw”], p= discoverable, observable]�

Multicast GET coap://224.0.1.187:5683/oic/res�

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GET and PUT requests

Unicast PUT coap://192.168.1.1:9000/a/light PayLoad: [state=1;dim=50]�

Unicast response

Status = Success�

Unicast GET coap://192.168.1.1:9000/a/light�

Unicast response

[URI: /a/light; state = 0, dim = 0]�

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OBSERVE and Notify

Notify Observers

[URI: /a/light; state = 0, dim = 0, sequence #: 1]�

Unicast GET coap://192.168.1.1:9000/a/light; Observe_option= 0�

Unicast response

[URI: /a/light; state = 1, dim = 50]�

Constrained environment characteristics

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•  RFC 7228

Must accommodate (at a minimum) OS + Network stack + drivers +

IoTivity-Constrained application

Constrained device classes

Name Data size (e.g., RAM) Code size (e.g., Flash)

Class 0, C0 << 10 KiB << 100 KiB

Class 1, C1 ~ 10 KiB ~ 100 KiB

Class 2, C2 ~ 50 KiB ~ 250 KiB

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•  Low RAM and flash capacity

•  Low power CPU with low clock cycle

•  Battery powered devices

Hardware

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•  Lightweight OS

•  No dynamic memory allocation

•  Many options (OS, network stack, …) -> API fragmentation

•  Execution context design and scheduling strategy

Software

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•  OCF roles, resource model, methods, data model, protocol and flows

•  CoAP Block-wise transfers (RFC 7959)

•  Application pre-configures MTU size for specific device / deployment

•  Reduce buffer allocations in the network and link layers

•  OCF security model

•  Onboarding, provisioning and access control*

*Refer to the OCF Security spec at https://openconnectivity.org/resources/specifications

IoTivity-Constrained features

IoTivity-Constrained architecture

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•  OS-agnostic core

•  Abstract interfaces to platform functionality

•  Rapid porting to new environments

•  Static memory allocation

•  Modular and configurable

Architectural goals

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Architecture

Embedded IoT

Application

On {Zephyr, Contiki, RIOT, Mynewt, Linux, …}

Zephyr

Contiki

RIOT

Linux

IoTivity-Constrained

Core

Clock

PRNG

Connectivity

Persistent Storage

Mynewt

Abstract Interfaces

Concrete Implementations

of Interfaces

IoTivity-Constrained Framework

Ports

APIs

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Core block Application APIs

OCF Client Role

Memory Management

Event Queue

OCF Server Role

Resource Model

Messaging

Security

Interact uniformly with Interface

implementations for all ports

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Event loop execution

Security

Messaging

Resource Layer

Embedded IoT

Application

Connectivity

Callbacks

Interrupt events

CoAP

while(…) { oc_main_poll() }

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Idle mode and signaling ... // Initialize a semaphore while (1) {

oc_clock_time_t next_event = oc_main_poll(); // next_event is the absolute time of the next scheduled // event in clock ticks. Meanwhile, do other tasks // or sleep (e.g., wait on semaphore) ... // Framework invokes a callback when there is new work static void signal_event_loop(void) {

// Wake up the event loop (e.g., signal the semaphore) }

Porting IoTivity-Constrained

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IoTivity-Constrained

Core

Clock

PRNG

Connectivity

Persistent Storage

Abstract Interfaces

IoTivity-Constrained Framework

Platform Abstraction

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Zephyr adaptation

APIs: Clock, Semaphore, PRNG, Networking, Flash

UDP/IP

802.15.4 Bluetooth Ethernet

Drivers, BSP

Kernel

Hardware Platform

IoT application

IoTivity-Constrained Core

Zephyr Port: Adaptation Layer

IoTivity-Constrained

Zephyr RTOS

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Clock // Set clock resolution in IoTivity-Constrained’s configuration // file: config.h #define OC_CLOCK_CONF_TICKS_PER_SECOND (...) typedef uint64_t oc_clock_time_t; // timestamp field width // Declared in port/oc_clock.h // Implement the following functions using the platform/OS’s // APIs, For eg. on Linux // using clock_gettime() void oc_clock_init(void); oc_clock_time_t oc_clock_time(void);

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•  oc_message_t contains remote endpoint information (IP/Bluetooth address), and a data buffer

Connectivity // Declared in port/oc_connectivity.h // Implement the following functions using the platform’s // network stack. int oc_connectivity_init(void); void oc_connectivity_shutdown(void); void oc_send_buffer(oc_message_t *message); void oc_send_discovery_request(oc_message_t *message); uint16_t oc_connectivity_get_dtls_port(void);

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•  Capture incoming messages by polling or with blocking wait in a separate context and construct an oc_message_t object

•  Message injected into framework for processing via oc_network_event()

•  Based on nature of OS or implementation, might require synchronization

Connectivity events

void oc_network_event_handler_mutex_init(void);

void oc_network_event_handler_mutex_lock(void);

void oc_network_event_handler_mutex_unlock(void);

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PRNG // Declared in port/oc_random.h // Implement the following functions to interact with the // platform’s PRNG void oc_random_init(void); unsigned int oc_random_value(void); void oc_random_destroy(void);

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Persistent storage // Declared in port/oc_storage.h

// Implement the following functions to interact with the

// platform’s persistent storage

// oc_storage_read/write must implement access to a key-value store

int oc_storage_config(const char *store_ref);

long oc_storage_read(const char *key, uint8_t *buf, size_t size);

long oc_storage_write(const char *key, uint8_t *buf, size_t size);

Building Applications

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•  Implemented in a set of callbacks

•  Initialization (Client / Server)

•  Defining and registering resources (Server)

•  Resource handlers for all supported methods (Server)

•  Response handlers for all requests (Client)

•  Entry point for issuing requests (Client)

•  Run event loop in background task

•  Framework configuration at build-time (config.h)

Application structure

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Background task in application main() { static const oc_handler_t handler = {.init = app_init, .signal_event_loop = signal_event_loop, .register_resources = register_resources }; ... oc_main_init(&handler); ... while (1) { oc_clock_time_t next_event = oc_main_poll(); ...

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Initialization

•  Populate standard OCF resources (platform / device)

void app_init(void) { oc_init_platform("Intel", NULL, NULL); oc_add_device("/oic/d", "oic.d.light", "Lamp", "1.0", "1.0", NULL, NULL); }

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Defining a resource .... void register_resources(void) { oc_resource_t *res = oc_new_resource("/a/light", 1, 0); oc_resource_bind_resource_type(res, "core.light"); oc_resource_bind_resource_interface(res, OC_IF_R); oc_resource_set_default_interface(res, OC_IF_R); oc_resource_set_discoverable(res, true); oc_resource_set_observable(res, true); oc_resource_set_request_handler(res, OC_GET, get_light, NULL); oc_add_resource(res); }

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Resource handler .... bool light_state; int brightness; .... static void get_light(oc_request_t *request, oc_interface_mask_t interface, ...) { // Call oc_get_query_value() to access any uri-query oc_rep_start_root_object(); oc_rep_set_boolean(root, state, light_state); oc_rep_set_int(root, brightness_level, brightness); oc_rep_end_root_object(); oc_send_response(request, OC_STATUS_OK); }

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Resource discovery oc_do_ip_discovery("oic.r.light", &discovery, NULL); .... oc_server_handle_t light_server; char light_uri[64]; ... oc_discovery_flags_t discovery(..., const char *uri, ..., oc_server_handle_t *server, ,...) { strncpy(light_uri, uri, strlen(uri)); memcpy(&light_server, server, sizeof(oc_server_handle_t)); return OC_STOP_DISCOVERY; // return OC_CONTINUE_DISCOVERY to review other resources }

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Issuing a request // Populated in the discovery callback oc_server_handle_t light_server; char light_uri[64]; ... oc_do_get(light_uri, &light_server, “unit=cd”, &get_light, LOW_QOS, NULL); ...

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Response handler void get_light(oc_client_response_t *data) { oc_rep_t *rep = data->payload; while (rep != NULL) { // rep->name contains the key of the key-value pair switch (rep->type) { case BOOL: light_state = rep->value_boolean; break; case INT: brightness = rep->value_int; break; } rep = rep->next; } }

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•  Set at build-time in a file config.h

•  Number of resources

•  Number of payload buffers and maximum payload size

•  Memory pool sizes

•  MTU size (for block-wise transfers)

•  Number of of DTLS peers

•  DTLS connection timeout

•  …

Framework configuration

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•  make%[BOARD=<type>]%menuconfig%

•  Stack size for main thread

•  Network stack options •  IPv6, UDP, 6LoWPAN, 6LoWPAN_IPHC

•  Number of network contexts (sockets)

•  Number of network RX/TX buffers, data size

•  Bluetooth host options: L2CAP CoC, GATT, master/slave modes

•  Layer 2 options: IEEE 802.15.4, Bluetooth LE, Ethernet

•  PRNG implementation

Project configuration

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•  Transport UDP/IPv6 over BLE L2CAP (RFC 7668)

•  Build 6LN with IPv6, 6Lo_IPHC, BT peripheral mode and L2CAP CoC

•  Use sample IPSS for connection setup

•  Supported on Arduino 101*

•  Test communication with Linux (>= 3.16) as master/central

* https://www.zephyrproject.org/doc/boards/x86/arduino_101/doc/board.html#arduino-101

IPv6 over BLE (IPSP) support

Conclusion

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•  Growing interest from community and prospective OCF vendors

•  OCF standards compliance; participate in OCF Plugfest

•  Motivate definition of constrained device profile in OCF spec

•  Investigate special requirements of industrial and healthcare verticals

•  Addition of independent, higher-level components

•  We welcome your contributions!

Summary and plans

Questions?

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Source code: https://gerrit.iotivity.org/gerrit/gitweb?p=iotivity-constrained.git

IoTivity mailing list: iotivity-dev@lists.iotivity.org

Kishen Maloor

kishen.maloor@intel.com

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